Promising Sorbent Research Articles

Zwitterionic cellulose as a promising sorbent for anionic and cationic dyes

This work aimed to develop zwitterionic cellulose with a versatile potential for removing anionic and cationic dyes. A grafting degree of 22% in a 3:2 ratio of the anionic and cationic groups was determined by elemental analysis. Spectroscopic characterization by carbon 13 Nuclear Magnetic Resonance (13C NMR) confirmed the zwitterionic functionalization of cellulose. Removal tests showed that zwitterionic cellulose could interact with different dyes (Congo red, Crystal violet, Mordant blue 9, Malachite green, Xylidine ponceau, and Reactive black 5), achieving from 2 to 14-fold of removal at tested conditions.

Improved CO2 adsorption capacity and fluidization behavior of silica-coated amine-functionalized multi-walled carbon nanotubes

The adsorption capacity and fluidization behavior of silica-coated amine-functionalized multi-walled carbon nanotubes (MWCNTs) were studied in this work. The coupling of both studies is fundamental for the practical application of CO2 sorbents in fluidized beds. Sorbents were prepared by hydrolysis of tetraethylorthosilicate (TEOS) onto acid-treated multi-walled carbon nanotubes followed by impregnation with monoethanolamine (MEA). The effects of different loading amounts of MEA and TEOS on CO2 uptake were investigated using thermogravimetric analysis under a simulated flue gas composed of 15%CO2/85% N2. At the optimal loadings of TEOS (30 ml) and MEA (30 wt%) on MWCNTs, 2.67 wt% of CO2 was captured at 25 °C, while the adsorption capacity of the pristine MWCNTs before any modification was negligible. Adsorption/desorption tests repeated 25 times also showed that the prepared sorbent has excellent stability during the cyclic operation; 9.42% reduction of the uptake was reported. Fluidizability of the most promising sorbent was also assessed when adding hydrophobic silica nanoparticles (NPs). Maximum bed expansion of 3.9 was achieved in the presence of 7.5 wt% silica NPs which was comparable by the amount of 2.24 belonged to raw MWCNTs. Enhancement of fluidity may be attributed to the decreased van der Waals attraction forces between the particles of sorbent. Besides, the CO2 adsorption capacity of the sorbent mixed with 5 wt% silica NPs was surprisingly increased by approximately 8%, reaching ~3 wt% of CO2.

Potassium hydroxide-modified algae-based biochar for the removal of sulfamethoxazole: Sorption performance and mechanisms

Biochar has been deemed one of the most promising sorbents for the removal of organic pollutants from aqueous solution. In this study, potassium hydroxide-modified Enteromorpha prolifera biochars (PEBCs) were prepared for the first time and applied for efficient sorption of a typical antibiotic, sulfamethoxazole (SMX). The characteristics of PEBCs, including morphology, pore structure, graphitization degree, surface functional groups, and surface element composition, were investigated. Moreover, sorption kinetic and isotherm experiments were carried out to explore the sorption process, performance, and mechanisms. The maximum sorption capacity for SMX can reach 744 mg g−1, which is much higher than that reported for sorbents. The sorption of SMX onto PEBCs was controlled by both physical and chemical processes. Moreover, pore filling, hydrogen bonding, partitioning, π-π stacking, and electrostatic interactions were possible sorption mechanisms. This study indicated that the structure and properties of algal biochar can be further improved by potassium hydroxide modification at high temperature and applied as an excellent sorbent for the removal of antibiotics from aqueous solution.

Battling Chemical Weapons with Zirconium Hydroxide Nanoparticle Sorbent: Impact of Environmental Contaminants on Sarin Sequestration and Decomposition.

The promising reactive sorbent zirconium hydroxide (ZH) was challenged with common environmental contaminants (CO2, SO2, and NO2) to determine the impact on chemical warfare agent decomposition. Several environmental adsorbates rapidly formed on the ZH surface through available hydroxyl species and coordinatively unsaturated zirconium sites. ZH decontamination effectiveness was determined using a suite of instrumentation including in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor sarin (GB) decomposition in real time and at ambient pressure. Surface products were characterized by ex situ X-ray photoelectron spectroscopy (XPS). The adsorption enthalpies, entropies, and bond lengths for environmental contaminants and GB decomposition products were estimated using density functional theory (DFT). Consistent with the XPS and DRIFTS results, DFT simulations predicted the relative stabilities of molecular adsorbates and reaction products in the following order: CO2 < NO2 < GB ≈ SO2. Microbreakthrough capacity measurements on ZH showed a 7-fold increase in the sorption of NO2 vs SO2, which indicates differences in the surface reactivity of these species. GB decomposition was rapid on clean and CO2-dosed ZH and showed reduced decomposition on SO2- and NO2-predosed samples. Despite these findings, the total GB sorption capacity of clean and predosed ZH was consistent across all samples. These data provide insight into the real-world use of ZH as a reactive sorbent for chemical decontamination applications.

Envelopes with microplastics generated from recycled plastic bags for crude oil sorption

AbstractOil spill accidents in marine environments and the lack of disposal of post‐consumer plastic are environmental problems worldwide. This study presents a sustainable alternative for both issues through envelopes filled with microplastics (MPs) from recycled bags for the sorption of spilled crude oil. Through particle size analysis by three different sieves (4, 9, and 20 mesh), different MP sizes were characterized by scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), density, contact angle (CA), and Fourier‐transform infrared spectroscopy (FTIR). According to their sizes, the MPs were distributed in envelopes and submitted to crude oil sorption capacity and efficiency evaluation. Three MP particle sizes were obtained (from the largest to the smallest, according to the sieve mesh, MP4, MP9, and MP20). SEM images of samples exhibited irregular and porous surfaces, and MP4 had the smallest pore size (8.6 μm). BET showed that MP4 had the highest surface area (0.074 m2/g). The CA &gt; 90° exposed that all samples were hydrophobic. FTIR spectrum demonstrated that the samples from the recycled bags were made of high density polyethylene (HDPE). The MP4 envelopes also had the best crude oil sorption results in capacity and efficiency (1.73 g/g and 68%, respectively), being a promising recycled sorbent in crude oil spillage applications.

Evaluating the potential of KOH-modified composite biochar amendment to alleviate the ecotoxicity of perfluorooctanoic acid-contaminated sediment on Bellamya aeruginosa

Modified composite biochar offers a cost-effective solution for the remediation of contaminated sediments; however, few studies have evaluated the effects of modified composite biochar amendment on the ecotoxicity of contaminated sediment based on benthic macroinvertebrates. A 21-day sediment toxicity test was conducted using the freshwater snail Bellamya aeruginosa to examine the intrinsic ecotoxicity of a novel KOH-modified composite biochar (KOH-CBC) and its efficacy for reducing the bioavailability, uptake, and ecotoxicity of perfluorooctanoic acid (PFOA). It was found that KOH-CBC is toxic to B. aeruginosa, which may be attributed to its high polycyclic aromatic hydrocarbons (PAHs) content and alkalinity. The addition of KOH-CBC to PFOA-contaminated sediments can markedly reduce the bioavailability and uptake of PFOA by more than 90% and 50%, respectively, and subsequently alleviate the toxicity of PFOA to B. aeruginosa by at least 30%. Increasing the KOH-CBC dosage is not beneficial for further mitigating the toxicity of PFOA-contaminated sediments. Our findings imply that KOH-CBC is a promising sorbent for the in-situ remediation of PFOA-contaminated sediments. Application of acidified KOH-CBC at a dosage of approximately 1–3% will be sufficient to control the ecotoxicity of PFOA; however, its long-term environmental effects should be further validated.

Microsphere molecularly imprinted solid-phase extraction for diazepam analysis using itaconic acid as a monomer in propanol

Abstract Diazepam (DZP) is a benzodiazepine drug used as an anti-drug and sedative. It is often misused to induce or create euphoria in combination with other drugs (high or fly sensation) or administered alone. So far, screening for DZP abuse with sensitive analytical methods is needed, as its small concentrations make it difficult to detect. Increased sensitivity of the analytical method can be obtained by using a preparation method that selectively separates the analyte from the sample matrix. Molecularly imprinted polymer (MIP) is one of the preparation solutions with good selectivity, specificity, and sensitivity. MIP was made from DZP as a template, itaconic acid, and ethylene glycol dimethacrylate in a composition of 1:4:20. MIP was made by precipitation polymerisation to obtain microsphere polymer type. MIP had a binding capacity value of 0.0557 mg/g and followed the Freundlich isotherm. Application of the microsphere MIP on spiked blood serum resulted in a recovery of 105.63 ± 1.0% for MIP compared to 21.28 ± 0.4% for non-imprinted polymer, with the imprinting factor value reaching 4.96. Hence, MIP DZP with itaconic acid as a functional monomer and propanol as a porogen, fabricated by the precipitation polymerisation method, is a promising sorbent for DZP extraction in biological fluids.

Scalable synthesis of KNaTiO3-based high-temperature CO2 capture material from high titanium slag: CO2 uptake, kinetics, regenerability and mechanism study

KNaTiO3 is a novel type of solid CO2 sorbents with strong sorption capacity and excellent regenerability at high temperatures. However, the expensive titanium precursor hampers its implementation for industrial applications. Herein, advanced KNaTiO3 based CO2 sorbents were first fabricated directly from high titanate slag (HTS). Elemental mapping analysis reveals high dispersion of KNaTiO3 and the crystal structure of KNaTiO3 in KNaTiO3-HTS-3 almost unchanged even after 15 cycles. The carbonation conversion of KNaTiO3-HTS-3 preserved a highly commendable value even after 100 sorption/desorption cycles, outperforming pure KNaTiO3. In addition, this sorbent exhibited faster sorption rate at 700 °C. Dynamic simulation demonstrated that the sorption constants k1 and k2 are higher and the activation energy is lower than those of conventional high-temperature sorbents. The CO2 sorption capacity of KNaTiO3-HTS-3 only met a slight decrease from 15.7 to 14.6 wt% with the decreasing CO2 concentration from 100 to 10 vol%. Compared with traditional high temperature CO2 sorbents, KNaTiO3-HTS-3 shows a slower breakthrough time. The reaction mechanism process for the promising sorbent is proposed. The HTS-derived KNaTiO3-based high-temperature CO2 sorbent has outstanding CO2 uptake, excellent regenerability, fast reaction kinetics as well as low cost, offering bright prospects in practical applications.

Facile synthesis of novel tremella-like Mn0@Mn2O3 and its exceptional performance on removal of phosphate

Phosphorus is an essential nutrient for biological growth, but its excessive presence in water can lead to eutrophication. Reducing phosphorus concentrations is an important way to prevent eutrophication of surface water bodies. In this study, a novel zero-valent manganese (ZVM) Mn0@Mn2O3 sorbent was synthesized via a facile one-step reduction method at ambient temperature. The morphology and surface properties of the Mn0@Mn2O3 were analyzed by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Zeta potential analyzer, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The obtained amorphous sample consists of many small tremella-like particles. The as-prepared sorbent shows exceptional phosphate removal performance and has a maximum adsorption capacity of 113.7 mg-P/g at pH 7.0, superior to many reported adsorbents. The removal of phosphate is obviously pH-dependent and is favorable under near-neutral and weak-alkaline conditions (pH 6.5–8.5). The kinetics data fit well to the pseudo-second-order model. The coexisting SO42-, CO32- and Cl- have no great influence on phosphate sorption, whereas, the SiO32- shows negative effect at high concentration. The sorbent is effective for phosphate removal from real municipal wastewater. The results of ionic strength effect experiment, SEM, XRD, FTIR and XPS analyses reveal that the phosphate was mainly removed through surface precipitation and formation of inner-sphere surface complexes. The Mn0@Mn2O3 is a promising sorbent for phosphate removal from surface water and wastewater, owning to its exceptional performance, high selectivity, environmental friendliness and easy preparation.

Surface Modification of Reduced Graphene Oxide Beads: Integrating Efficient Endotoxin Adsorption and Improved Blood Compatibility.

As a pathogenic toxin, endotoxins are the culprit for endotoxemia and can be generally removed from the blood by hemoperfusion. Reduced graphene oxide (rGO) is a promising endotoxin sorbent for hemoperfusion owing to its excellent adsorption capacity, but it has the side effect of nonspecific adsorption and low blood compatibility. Polymyxin B (PMB) acts as an organic affinity ligand that can specifically bind endotoxins. As a natural anticoagulant, heparin (Hep) can reduce the risk of coagulation and improve the blood compatibility of materials. Herein, an rGO bead adsorbent was prepared by coupling with PMB and Hep and used for endotoxin adsorption; in this, polydopamine (pDA) served as an active coating for immobilization of PMB and further coupling with Hep. The physicochemical characteristics indicated that PMB and Hep were successfully immobilized on rGO beads with a hierarchical pore structure. PMB endowed rGO beads with higher adsorption capacity (143.84 ± 3.28 EU/mg) and good adsorption selectivity for endotoxins. Hep significantly improved the blood compatibility of rGO beads. These modified rGO beads also achieved good adsorption capacity and adsorption selectivity for endotoxins in plasma, serum, or blood. Therefore, rGO/pDA/PMB/Hep beads are potential adsorbents for endotoxins in hemoperfusion.

Capture of elemental mercury from flue gas over a magnetic and sulfur-resistant sorbent prepared from Fe-containing sewage sludge activated with sulfuric acid

By the pyrolysis of Fe-containing sewage sludge activated with sulfuric acid, a magnetic and sulfur-resistant sorbent (FSS-SA) was obtained, and it was used for capturing elemental mercury from flue gas. Sulfuric acid activation improved the pore structure, increased the contents of Fe3+, Oβ and polysulfide and promoted the redox activity of the sorbent, leading to the enhanced Hg0 removal activity. Both active oxygen and sulfur species derived from Fe2O3 and ferric polysulfide were the active sites for Hg0 removal. The increased surface acidity due to sulfuric acid activation suppressed the interaction of SO2 with FSS-SA and the polysulfide maintained the function of capturing Hg0 with SO2 presence. The Hg0 adsorption capacity of FSS-SA under simulated flue gas was estimated to be 14.8 mg/g. Meanwhile, FSS-SA exhibited superparamagnetic property with the saturation magnetization of 13.49 emu·g−1. It could be separated from fly ash mixture by using a magnetic separator. Utilizing the sludge for production of mercury sorbent can reduce the cost of sorbent and also help to find a way for resource utilization of the sewage sludge. FSS-SA might be a promising mercury sorbent due to its simple preparation method, low cost, magnetic property, good tolerance to SO2 and excellent performance.

High affinity lanthanum doped iron oxide nanosheets for phosphate removal

• New synthesis route leading to nano La(OH) 3 cluster interlayered iron oxides. • Sorbent affinity for phosphate increases with La content with partitioning coefficients up to 10 5 L/kg. • La doped sorbents show high selectivity for phosphate in presence of competing solutes. • Sorption of phosphate dominated by inner sphere La-O-P complexation. Phosphorus induced eutrophication of freshwaters is one of the great global challenges. As the critical threshold concentration for eutrophication is very low, there is a strong need for development of phosphate sorbents with high affinity and selectivity. Single sheet iron oxide (SSI), a nanomaterial prepared from oxidation and exfoliation of layered iron(II)-iron(III) hydroxide (green rust), is a fast reacting and promising sorbent. Phosphate sorption affinity and selectivity may be improved by incorporation of lanthanum (La) in the structure. Lanthanum was added during SSI synthesis resulting in La-SSIs with 0 to 22.5 wt% of La content. XPS and EXAFS showed all La was present as La(OH) 3 nanoclusters between iron hydroxide layers and on the surface of SSI. The sorbent showed fast phosphate sorption with 90% completion within 30 min and high stability with minimal La leaching. All La-SSI nanomaterials showed better sorption affinity than non-doped SSI, and the La-SSI with the highest La content showed an extreme affinity with K d of 10 5 L/kg at solution concentration of 0.1 mg P/L. The sorption affinity was not seriously affected by pH. The La-SSIs showed high selectivity for phosphate with<10% reduction in phosphate sorption in presence of co-existing solutes (Cl – , NO 3 – , SO 4 2- , HCO 3 – and humic acid). Similar high affinity and selectivity was seen for phosphate sorption in real natural waters. The main phosphate sorption mechanism is attributed to inner sphere Fe-O-P and La-O-P surface complexation. In conclusion La doping turns SSI into a high-affinity and selectivity sorbent that has potential for polishing low-phosphate yet eutrophying natural waters such as drainage and lake waters.

Iodine Capture with Mechanically Robust Heat-Treated Ag-Al-Si-O Xerogel Sorbents.

Various radionuclides are released as gases during reprocessing of used nuclear fuel or during nuclear accidents including iodine-129 (129I) and iodine-131 (131I). These isotopes are of particular concern to the environment and human health as they are environmentally mobile and can cause thyroid cancer. In this work, silver-loaded heat-treated aluminosilicate xerogels (Ag-HTX) were evaluated as sorbents for iodine [I2(g)] capture. After synthesis of the base NaAlSiO4 xerogel, a heat-treatment step was performed to help increase the mechanical integrity of the NaAlSiO4 gels (Na-HTX) prior to Ag-exchanging to create Ag-HTX xerogels. Samples were characterized by powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, gravimetric iodine loading, nanoindentation, and dynamic mechanical analysis. The structural and chemical analyses of Ag-HTX showed uniform distribution of Ag throughout the gel network after Ag-exchange. After I2(g) capture, the AgI crystallites were observed in the sorbent, verifying chemisorption as the primary iodine capture mechanism. Iodine loading of this xerogel was 0.43 g g–1 at 150 °C over 1 day and 0.52 g g–1 at 22 °C over 33 days. The specific surface area of Ag-HTX was 202 m2 g–1 and decreased to 87 m2 g–1 after iodine loading. The hardness of the Na-HTX was >145 times higher than that of the heat-treated aerogel of the same starting composition. The heat-treatment process increased Young’s modulus (compressive) value to 40.8 MPa from 7.0 MPa of as-made xerogel, demonstrating the need for this added step in the sample preparation process. These results show that Ag-HTX is a promising sorbent for I2(g) capture with good iodine loading capacity and mechanical stability.

Vermiculite modified with alkylammonium salts: characterization and sorption of ibuprofen and paracetamol

In this work, the clay mineral vermiculite (VT) was treated using the bromide form of quaternary alkylammonium salts—ethylhexadecyldimethylammonium (EHDDMAB), hexadecyltrimethylammonium (HDTMAB), tetradecyltrimethylammonium (TDTMAB) and tetrabutylammonium (TBAB), in order to obtain the organo-vermiculites (OVT) named as VT-EHDDMA, VT-HDTMA, VT-TDTMA and VT-TBA, respectively. These sorbents and the precursor VT were characterized using several techniques which allowed to infer the intercalation of the alkylammonium salts in the interlayer space of VT, except VT-TBA, and these materials were evaluated as sorbents for ibuprofen and paracetamol. VT and OVT presented no significant interactions with paracetamol and sorbed less than 10% of the initial concentration. On the other hand, two OVT sorbents demonstrated high efficiency in the sorption of ibuprofen, and the maximum percent removal was higher than 92% for VT-EHDDMA and VT-HDTMA, with a maximum sorption capacity of 52 ± 2 mg g−1 (VT-EHDDMA) and 54 ± 2 mg g−1 (VT-HDTMA), whereas 16 ± 2 mg g−1 was observed for VT. These results suggest that the low-cost OVT could be considered as appropriate sorbent for ibuprofen removal from aqueous medium, and probably as a promising sorbent for drugs of a wide polarity range, with neutral, acid and basic characteristics.

Elemental mercury capture from flue gas by magnetic recyclable Fe6Mn1-xCexOy sorbent. Part 1. Performance evaluation and regeneration

A series of Ce doped Fe-Mn magnetic sorbents (Fe6Mn1-xCexOy) were prepared by using the co-precipitation method. The mercury removal performance evaluation and thermal regeneration of Fe6Mn1-xCexOy sorbent was conducted in a fixed-bed system. Combining with the characterization of N2 adsorption, X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS), the structure–activity relationship and the mechanism of circulating mercury removal by Fe6Mn1-xCexOy sorbent was analyzed. The results show that the Fe6Mn0.8Ce0.2Oy sorbent displays the best mercury removal capability, because Ce doping modifies the pore structure of sorbent, but excessive Ce addition reduces the active component of Mn. Both O2 in flue gas and low temperature are beneficial to mercury removal by Fe6Mn0.8Ce0.2Oy sorbent, because O2 can supplement the consumed lattice oxygen and Ce doping promotes the oxidation activity of lattice oxygen at low temperature. During mercury removal process, gas phase Hg0 is oxidized to Hg2+ by Mn4+ reducing to Mn3+, and combining with adsorbed O to form HgO. During thermal regeneration, part of Mn3+ is re-oxidized to Mn4+ by O2 in flue gas as well as Ce3+. After 6 cycles of mercury removal and thermal regeneration, the Fe6Mn0.8Ce0.2Oy sorbent still keep stable magnetism and high mercury removal capability. Therefore, the Fe6Mn0.8Ce0.2Oy sorbent is a promising sorbent for cyclic mercury removal from coal-fired flue gas.

Comparative study on methylene blue adsorption behavior of coffee husk-derived activated carbon materials prepared using hydrothermal and soaking methods

Coffee husk, a carbonaceous precursor and common agricultural waste in Vietnam, was utilized to produce activated carbon by hydrothermal carbonization (HTC) with high adsorption capacity for pollutants. The characteristics and adsorption capacity of the hydrochar produced at the first HTC step (180 °C, 6 h) were subjected to further hydrothermal activation (130 °C for 2 h) with a low concentration of potassium hydroxide (ACHC-KOH 1 M), and directly soaked in KOH medium (ACHC-KOH 1:1). The surface area of the activated hydrochar obtained was significantly increased from 33.7 m2/g (raw hydrochar) to 703.9 m2/g for ACHC-KOH 1 M and 743.8 m2/g for ACHC- KOH 1:1, respectively. The maximum methylene blue (MB) adsorption achieved by the activated carbon materials were 357.38, 314.05, and 103.62 mg/g by ACHC-KOH 1 M, ACHC-KOH 1:1, and raw hydrochar, respectively. Adsorption kinetics and isotherms were employed to explain the MB adsorption process. Adsorption data of MB on ACHC-KOH 1 M and ACHC-KOH 1:1 fitted well with Langmuir adsorption isotherm and pseudo-second-order kinetic model. The results show that coffee husk-based activated carbon is a promising sorbent for the removal of MB from aqueous solutions. Compared to other carbonization methods, the HTC method has advantages of using a low temperature and concentration of KOH.

Pomegranate peel waste biomass modified with H3PO4 as a promising sorbent for uranium(VI) removal

Modified pomegranate peel was utilized as a sorbent for the biosorption of uranium(VI) from the aqueous solution. The biosorbent was characterized by infrared spectroscopy with Fourier transformation, energy dispersive X-ray fluorescence spectrometry, particle size analyser and determination of pHpzc. “Under optimized experimental conditions” the maximum adsorption capacity was 93.40 mg L−1. The equilibrium data fitted well to the Freundlich’s and Temkin’s isotherm model. Calculated data from applied kinetics model showed best agreement to the pseudo-second order model. Thermodynamic study showed the adsorption process is endothermic and nonspontaneous.

Synthesis and Application of Zwitterionic Magnetic Molecularly Imprinted Polymer for Selective Removal of Fluoroquinolones from Aqueous Solution

Background: Although molecularly imprinted polymers (MIPs) have now been widely utilized for the sample pretreatment, chromatography separation and removal of pollutants, conventional MIPs are still lack of satisfactory compatibility with water, thus leading to poor molecular recognition for target analytes in aqueous solutions. This aim of study was to prepare the watercompatible MIPs. Methods: The zwitterionic MMIPs were synthesized on vinyltrimethoxysilane-coated Fe3O4 (Fe3O4-VTMS) through a surface imprinting process by using levofloxacin (LEV) as a template, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SPE) as a functional monomer, N, N-methylene-bis-acrylamide (MBA) as a crosslinker and potassium persulfate as an initiator. Results: The prepared zwitterionic LEV-MMIPs were characterized by Fourier transform infrared spectrometry, X-ray diffraction, vibrating sample magnetometry, scanning electron microscopy and water contact angle test. The characterization results showed that zwitterionic LEV-MMIPs exhibited good magnetic responsiveness and super-hydrophilicity (the contact angle is 0°). The optimum pH for binding LEV was found to be 6.0 and the binding isotherm followed the Langmuir isotherm model of monolayer adsorption. The binding process was very fast and the pseudo-second-order model fitted well with the kinetic data. The adsorption capacity of these zwitterionic MMIPs was 54.30 mg g-1 with a selectivity factor of 1.6 compared to the magnetic non-imprinted polymers (MNIPs). Their feasibility for removing fluoroquinolones (FQs) from the environmental sample was demonstrated using pearl river water spiked with LEV, gatifloxacin, ciprofloxacin and lomefloxacin. The zwitterionic LEV-MMIPs could be reused at least five times with a removal efficiency of more than 80% for the selected FQs. Conclusion: The prepared zwitterionic LEV-MMIP is a promising sorbent for rapid, selective and efficient removal of fluoroquinolones from aqueous medium.

Enhanced adsorption of Cu(II) and Zn(II) from aqueous solution by polyethyleneimine modified straw hydrochar.

Heavy metals removal from aqueous phase by adsorption technique has recently attracted a considerable interest. Although various adsorbing materials have been developed, introducing more functional groups is considered as the most efficient way to promote the adsorption capacity of the selected adsorbent. However, this approach is usually limited in costly modification precursor and unguaranteed loading efficacy. In this study, waste corn straw was converted to adsorbent precursor by hydrothermal carbonization. The obtained hydrochar (HC) was chemically activated before being modified by polyethyleneimine (PEI). Multiple analysis methods including Scanning Electron Microscopy, Fourier Transform Infrared analysis, and X-ray Photoelectron Spectroscopy analysis verified the alkali activated hydrochar (alkali-HC) was more efficacy to enhance PEI grafting than acid activation. Based on this, the modified HC materials obtained a better adsorption performance. The sorption process of Cu(II) and Zn(II) on the acid-PEI-HC, alkali-PEI-HC, and pristine HC fitted the pseudo second order kinetic and Freundlich model well, and was dominated by chemisorption. Among these adsorbents, the adsorption capacity of alkali-PEI-HC to metal ions was the maximum, which was 207.6mg/g to Zn(II) and 56.1mg/g to Cu(II) at 298K. Regeneration tests showed a result of no less than 60% of its removal capacity was achieved after five cycles. Therefore, alkali-PEI-HC performed as a promising composite sorbent for metal ions. In addition, the study described here has provided a new basis for the utilization of hydrochar (1.08 kWh kg-1) derived from agricultural resources as a promising adsorbent precursor.

Synergistic role of bulk carbon and iron minerals inherent in the sludge-derived biochar for As(V) immobilization

Sludge-derived biochar has been considered as a promising sorbent for As(V) due to its high content of Fe. However, role of different endogenous iron minerals and the bulk carbon in this process remained unclear. Here, biochar with different Fe content and species were prepared from two types of sludge (SSA and SSB) at 350 °C or 700 °C for As(V) immobilization. Although SSB biochar had considerable Fe (3.6%-8.6%), they showed limited sorption capacity for As(V) due to the electrostatic repulsion related to the negatively charged surface at the experimental pH. By contrast, SSA biochar demonstrated superior sorption abilities for As(V) with the maximum capacities of 60.2–90.2 mg g−1. Amorphous iron determined the removal of As(V) by SSA350 due to the adsorption and the co-precipitation of released Fe2+ with H2AsO4-, which accounted for 77.6% and 22.4%, respectively. For SSA700, iron minerals were converted to more crystalline species, including γ-FeOOH, Fe4(O,OH,SO4)9, and Fe2(SO3)3·xH2O, and the co-precipitation with As(V) caused 74.6% of As(V) removal by SSA700. The bulk carbon of biochar was proved to serve as heterogeneous nucleation sites for the co-precipitation, showing its synergistic effect with iron on As(V) removal, which raised the removal efficiency from 0.9–2.9% by Fe2+ alone to 13.9–25.5% by Fe2+ co-existing with bulk carbon. Findings of this study not only demonstrate the importance of iron species in biochar to As(V) removal, but also provide new insights on the synergistic effect of iron interaction with bulk carbon.